The present invention relates to an optical information recording apparatus and an optical information recording method for recording information onto an optical information recording medium by using holography, optical information reproduction apparatus and an optical information reproduction method for reproducing information from an optical information recording medium by using holography, and optical information recording and reproduction apparatus for recording information onto an optical information recording medium as well as reproducing information from an optical information recording medium by using holography.
Holographic recording whereby information is recorded onto an optical information recording medium by using holography is accomplished in such a manner that a beam carrying image information (hereinafter referred to as an information beam) and a reference beam inside the optical information recording medium are overlapped and a resulting interference pattern is written onto the optical information recording medium. When the recorded information is reproduced, a reference beam is irradiated onto the optical information recording medium to reproduce the image information by way of diffraction using the interference pattern.
Such holographic recording is characterized by recording information by way of a three-dimensional pattern in the direction of thickness of an optical information recording medium and is also referred to as volume holography recording. By increasing the thickness of the recording layer of an optical information recording medium, it is possible to increase the diffraction efficiency. Further, by recording information in a multiple fashion through angular multiplexing, it is possible to increase the recording capacity.
One of the related art hologram recording and reproduction methods uses Fourier-transform processing to record and reproduce information (Japanese Patent Laid-Open No. 2002-123161). The method is described below referring to FIG. 26. As shown in FIG. 26, a luminous flux 12 emitted from a laser light source 11 is split into an information beam 12a and a recording reference beam 12b by a beam splitter 13. The information beam 12a has its beam diameter expanded by a beam expander 25 and irradiated as a parallel beam onto a spatial light modulator (SLM) 15. The spatial light modulator (SLM) 15 comprising a transmission TFT liquid crystal display (LCD) panel receives as electric signal recording data converted into a signal by an encoder and arranges the signal onto a two-dimensional plane to generate two-dimensional digital pattern information and form a pattern of light and dark dots on the plane. A single item of two-dimensional digital pattern information is called page data.
The information beam 12a, passing through the spatial light modulator (SLM) 15, undergoes optical modulation and includes a data signal component. The information beam 12a including the dot pattern signal component passes through a Fourier transform lens 30 apart by its focal length “f”. In this process, the dot pattern signal component of the information beam 12a undergoes Fourier-transform processing and is condensed into an optical information recording medium.
The recording reference beam 12b split by the beam splitter 13 is guided into the optical information recording medium by mirrors 17, 18 and crosses the information beam 12a inside the optical information recording medium to form an interference pattern, which is recorded as a modulation in the refractive index.
In angular-multiplexed recording, the optical information recording medium is rotated to vary the relative angle between the recording reference beam 12b and the optical information recording medium. In this example, page data #1 through #n undergoes angularly multiplexed recording onto the same optical information recording medium. Based on the page data #1, the light-transmission or light-interception state is selected per pixel by the spatial light modulator (SLM) 15 to generate the spatially modulated information bean 12a and irradiate the information beam 12a onto the optical information recording medium. At the same time, a recording reference beam 12b is irradiated from a direction θ1 (not shown) onto the optical information recording medium and an interference pattern produced by overlaying the information beam 12a on the recording reference beam 12b in the optical information recording medium is recorded.
In recording the next page data #2, the optical information recording medium is rotated by a predetermined angle and a recording reference beam 12b is irradiated at an angle θ2 different from θ1 and the recording reference beam 12b is overlaid on the information beam 12a to perform multiple recording of information onto the same optical information recording medium. Similarly, in recording of the remaining page data #3 through #n, the recording reference beam 12b is irradiated at different angles θ3 through θn to perform multiple recording of information.
In reproduction of information, the optical path of the information beam 12a is intercepted by the spatial light modulator (SLM) 15 to radiate the recording reference beam 12b alone onto the optical information recording medium. In reproduction of information, control is made to vary the angle of the optical information recording medium so that the same incident angle as that of the recording reference beam 12b in recording of page data to be reproduced will be obtained.
On the opposite side of the optical information recording medium on which the recording reference beam 12b is irradiated appears are production beam which reproduces a Fourier-transform image having a recorded dot pattern. The reproduction beam is guided to the Fourier-transform lens 30b and inversely Fourier transformed to reproduce a dot pattern signal. The dot pattern signal is received by a light receiving element 20 such as a CCD (charge coupled device) and further converted to an electric digital data signal. The digital data signal is then sent to a decoder and original data is reproduced therein.
Optical information recording and reproduction apparatus is known which irradiates an information beam and a reference beam from the same side of an optical information recording medium (Japanese Patent Laid-Open No. 10-0124872/(1998)). The optical information recording and reproduction apparatus irradiates an information beam and a reference beam coaxially onto an optical information recording medium as well as condenses the information beam and the reference beam so that they will be brought into focus on the surface of the reflective layer in the optical information recording medium in order to record and reproduce information. In reproduction of information, the optical information recording and reproduction apparatus irradiates the reference beam onto the optical information recording medium and receives, on a light receiving element such as a CCD, a beam produced by reflection of a reproduction beam generated from the reference beam in order to reproduce the original data.
The optical information recording and reproduction apparatus described in the Japanese Patent Laid-Open No. 2002-123161 comprises an optical system including a light source 11 and a spatial light modulator (SLM) 15 and a light receiving element 20 for receiving a reproduction beam are arranged opposite to each other across an optical information recording medium.
This complicates the optical system of the entire optical information recording and reproduction apparatus, and it has been difficult to scale down the apparatus.
The optical information recording and reproduction apparatus described in the Japanese Patent Laid-Open No. 10-124872/(1998) condenses an information beam and a reference beam so that they will be brought into focus on the surface of the reflective layer in the optical information recording medium in order to record and reproduce information.
Thus, in case the optical information recording medium is moved or changed, it is necessary to condense the information beam and the reference beam again so that they will be brought into focus on the surface of the reflective layer in the optical information recording medium. That is, it is necessary to control the position of each of the optical system and the optical information recording medium to perform re-focusing.